IGCSE Chemistry 0620 notes

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY EXAM QUESTIONS ? QUESTION 1 Which one of the following structures is correctly named? ? QUESTION 2 Organic compounds can have names that have the suffixes of -ane, -ene, -ol or -oic acid. How many of these have at least one double bond in their structure A 1  B 2  C 3  D 4 ? QUESTION 3 When the number of atoms in a molecule of a hydrocarbon increases, the amount of energy released when it burns increases. What is the correct order? less energy → more energy released A methane ethene ethane B ethene ethane methane C ethene methane ethane D methane ethane ethene > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK Head to savemyexams.co.uk for more questions and revision notes © copyright Save My Exams CIE IGCSE Chemistry Resources Page 14 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.2  FUNCTIONAL GROUP CHEMISTRY 14.2.1  ALKANES Alkanes: Properties & Bonding Alkanes • A homologous series of hydrocarbon compounds with only single carbon bonds, there are no C=C bonds present • General formula of alkanes: CnH2n + 2 • Alkanes are classified as saturated hydrocarbons as all the bonds in alkanes are single bonds • They are colourless compounds which have a gradual change in their physical properties as the number of carbon atoms in the chain increases • Alkanes are generally unreactive compounds but they do undergo combustion reactions, can be cracked into smaller molecules and react with halogens in the presence of light • Methane is an alkane and is the major component of natural gas • Methane undergoes complete combustion forming carbon dioxide and water: CH4 + 2O2 → CO2 + 2H2O The first three alkanes © copyright Save My Exams CIE IGCSE Chemistry Resources Page 15 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.2.1  ALKANES cont... EXTENDED ONLY Substitution Reaction of Alkanes with Halogens • In a substitution reaction, one atom is swapped with another atom • Alkanes undergo a substitution reaction with halogens in the presence of ultraviolet radiation In the presence of ultraviolet (UV) radiation, methane reacts with bromine in a substitution reaction Methane  +  Bromine  →  Bromomethane  +  Hydrogen Bromide CH4 Br2 CH3Br HBr 14.2.2  ALKENES Alkenes: Catalytic Cracking & Distinguishing from Alkanes Alkenes • A homologous series of hydrocarbon compounds with carbon-carbon double bonds (C = C) • General formula: CnH2n • All alkenes contain a double carbon bond, which is shown as two lines between two of the carbon atoms • This is the alkene functional group and is what allows alkenes to react in ways that alkanes cannot • Compounds that have a C=C double bond are also called unsaturated compounds. © copyright Save My Exams CIE IGCSE Chemistry Resources Page 16 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.2.2  ALKENES cont... The first three alkenes Manufacture of alkenes and hydrogen • Although there is use for each fraction obtained from the fractional distillation of crude oil, the amount of longer chain hydrocarbons produced is far greater than needed • These long-chain hydrocarbon molecules are further processed to produce other products • A process called catalytic cracking used to convert longer-chain molecules into short- chain and more useful hydrocarbons • Alkenes and hydrogen are produced from the cracking of alkanes • Kerosene and diesel oil are often cracked to produce petrol, other alkenes and hydrogen Explanation: • Cracking allows large hydrocarbon molecules to be broken down into smaller, more useful hydrocarbon molecules • Fractions containing large hydrocarbon molecules are heated at 600 – 700°C to vaporise them • Vapours will then pass over a hot catalyst of silica or alumina • This process breaks covalent bonds in the molecules, causing thermal decomposition reactions • As a result, cracking produces smaller alkanes and alkenes. The molecules are broken up in a random way which produces a mixture of alkanes and alkenes • Hydrogen and a higher proportion of alkenes are formed at temperatures of above 700ºC and higher pressure © copyright Save My Exams CIE IGCSE Chemistry Resources Page 17 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.2.2  ALKENES cont... The 10 carbon molecule decane is catalytically cracked to produce octane for petrol and ethene for ethanol Distinguishing between alkanes and alkenes • Alkanes and alkenes have different molecular structures • All alkanes are saturated and alkenes are unsaturated • The presence of the C=C double bond allows alkenes to react in ways that alkanes cannot • This allows us to tell alkenes apart from alkanes using a simple chemical test: Diagram showing the result of the test using bromine water with alkanes and alkenes © copyright Save My Exams CIE IGCSE Chemistry Resources Page 18 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.2.2  ALKENES cont... Explanation: • Bromine water is an orange coloured solution of bromine • When bromine water is shaken with an Alkane, it will remain as an orange solution as alkanes do not have double carbon bonds (C=C) so the bromine remains in solution • But when bromine water is shaken with an alkene, the alkene will decolourise the bromine water and turn colourless as alkenes do have double carbon bonds (C=C) • The bromine atoms add across the C=C double bond hence the solution no longer contains the orange coloured bromine • This reaction between alkenes and bromine is called an addition reaction Each carbon atom of the double bond accepts a bromine atom, causing the bromine solution to lose its colour Addition Polymerisation • Addition polymers are formed by the joining up of many small molecules called monomers • Addition polymerisation only occurs in monomers that contain C=C bonds • One of the bonds in each double bond breaks and forms a bond with the adjacent monomer • There are many types of polymers that are synthesized from alkene monomers • A common example is poly-ethene (polythene) which is the addition of many ethene monomers Polymerisation of ethene monomers to produce polythene © copyright Save My Exams CIE IGCSE Chemistry Resources Page 19 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.2.2  ALKENES cont... EXTENDED ONLY Further Addition Reactions Addition reactions of alkenes • Alkenes undergo addition reactions in which atoms of a simple molecule add across the C=C double bond • The reaction between bromine and ethene is an example of an addition reaction Bromine atoms add across the C=C in the addition reaction of ethene and bromine • Alkenes also undergo addition reactions with hydrogen in which an alkane is formed • These are hydrogenation reactions and occur at 150ºC using a nickel catalyst • Hydrogenation reactions are used to change vegetable oils into margarine to be sold in supermarkets Hydrogen atoms add across the C=C in the hydrogenation of ethene to produce an alkane • Alkenes also undergo addition reactions with steam in which an alcohol is formed. Since water is being added to the molecule it is also called a hydration reaction • The reaction is very important industrially for the production of alcohols and it occurs using the following conditions: © copyright Save My Exams CIE IGCSE Chemistry Resources Page 20 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.2.2  ALKENES cont... • Temperature of around 330ºC • Pressure of 60 – 70 atm • Concentrated phosphoric acid catalyst A water molecule adds across the C=C in the hydration of ethene to produce ethanol 14.2.3  ALCOHOLS Alcohols Alcohols • Family of organic compounds that all contain the -OH functional group • This is the group of atoms responsible for their chemical properties and reactions The first three alcohols Ethanol • Ethanol (C2H5OH) is one of the most important alcohols • It is the type of alcohol found in alcoholic drinks such as wine and beer • It is also used as fuel for cars and as a solvent • Alcohols burn in excess oxygen and produce CO2 and H2 • Ethanol undergoes combustion: CH3CH2OH + 3O2 → 2CO2 + 3H2O © copyright Save My Exams CIE IGCSE Chemistry Resources Page 21 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.2.3  ALCOHOLS cont... The manufacture of ethanol • There are two methods used to manufacture ethanol: • The hydration of ethene with steam • The fermentation of glucose • Both methods have advantages and disadvantages which are considered Hydration of ethene • A mixture of ethene and steam is passed over a hot catalyst of phosphoric acid at a temperature of 330°C • The pressure is used 60-70 atmosphere • The gaseous ethanol is then condensed into a liquid for use A water molecule adds across the C=C in the hydration of ethene to produce ethanol Fermentation of glucose • Sugar or starch is dissolved in water and yeast is added • The mixture is then fermented between 15 and 35°C with the absence of oxygen for a few days • Yeast contains enzymes that break down starch or sugar to glucose • If the temperature is too low the reaction rate will be too slow and if it is too high the enzymes will become denatured • The yeast respire anaerobically using the glucose to form ethanol and carbon dioxide: C6H12O6 + Enzymes → 2CO2 + 2C2H5OH • The yeast are killed off once the concentration of alcohol reaches around 15%, hence the reaction vessel is emptied and the process is started again • This is the reason that ethanol production by fermentation is a batch process. © copyright Save My Exams CIE IGCSE Chemistry Resources Page 22 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.2.3  ALCOHOLS cont... Comparing methods of ethanol production HYDRATION OF ETHENE FERMENTATION EQUIPMENT COMPLEX SET-UP REQUIRED SIMPLE EQUIPMENT NEEDED RAW USES NON-RENEWABLE USES RENEWABLE RESOURCES MATERIALS RESOURCES (CRUDE OIL) (SUGAR CANE) TYPE OF CONTINUOUS PROCESS - A BATCH PROCESS - EVERYTHING PROCESS STREAM OF REACTANT IS IS MIXED TOGETHER IN A CONSTANTLY PASSED OVER REACTION VESSEL AND THEN THE CATALYST. THIS IS MORE LEFT FOR SEVERAL DAYS. THAT EFFICIENT THAN A BATCH BATCH IS THEN REMOVED AND A PROCESS NEW REACTION IS SET UP - THIS IS INEFFICIENT RATE OF FAST VERY SLOW (SEVERAL DAYS) REACTION QUALITY OF PRODUCES PURE ETHANOL PRODUCES A DILUTE PRODUCT SOLUTION REQUIRING FURTHER PROCESSING ATMOSPHERIC NO GREENHOUSE GAS IS PRODUCED CARBON DIOXIDE PRODUCED EFFECTS BUT POLLUTANTS ARE FORMED WHICH IS A GREENHOUSE GAS FROM THE BURNING OF FOSSIL FUELS TO MAINTAIN HIGH TEMPERATURE REACTION HIGH TEMPERATURES AND LOW TEMPERATURES REQUIRED CONDITIONS PRESSURES REQUIRED, INCREASING THE ENERGY INPUT AND COST EXAM TIP Fermentation is an anaerobic process. Oxygen is not required for ethanol to be produced by fermentation. © copyright Save My Exams CIE IGCSE Chemistry Resources Page 23 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.2.4  CARBOXYLIC ACIDS Ethanoic Acid Carboxylic acids • These are a homologous series of organic compounds that all contain the same functional group: –COOH • They are colourless liquids which are weakly acidic and have typical acidic properties • They react with alkaline solutions, turn blue litmus red and form salts called ethanoates The first three carboxylic acids Ethanoic acid • Ethanoic acid is a typically weak acid and dissociates slightly in water, producing a mildly acidic solution • The equilibrium lies far to the left during ionization: CH3COOH ⇌ H+ + CH3COO– • Ethanoic acid reacts with the more reactive metals, hydroxides and carbonates Reactions of ethanoic acid • In the reaction with metals a metal salt and hydrogen gas are produced • For example in reaction with magnesium the salt magnesium ethanoate is formed: 2CH3COOH + Mg → (CH3COO)2Mg + H2 • In the reaction with hydroxides a salt and water are formed in a neutralisation reaction • For example in reaction with potassium hydroxide the salt potassium ethanoate is formed: CH3COOH + KOH → CH3COOK + H2O • In the reaction with carbonates a metal salt, water and carbon dioxide gas are produced • For example in reaction with potassium carbonate the salt potassium ethanoate is formed: 2CH3COOH + K2CO3 → 2CH3COOK + H2O + CO2 © copyright Save My Exams CIE IGCSE Chemistry Resources Page 24 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.2.4  CARBOXYLIC ACIDS cont... EXAM TIP The carbon atom in the -COOH functional group is counted as part of the molecule and not just the functional group. E.g. CH3CH2CH2COOH has 4 carbon atoms so is called butanoic acid, not propanoic acid. EXTENDED ONLY Ethanoic Acid & Esterification Reactions Making Carboxylic Acids Oxidation by fermentation • The microbial oxidation of ethanol will produce a weak solution of vinegar (ethanoic acid) • This occurs when a bottle of wine is opened as bacteria in the air (acetobacter) will use atmospheric oxygen from air to oxidise the ethanol in the wine: C2H5OH + O2 → CH3COOH + H2O • The acidic, vinegary taste of wine which has been left open for several days is due to the presence of ethanoic acid Oxidation with potassium manganate (VII) • Alcohols can also be oxidised to carboxylic acids by heating with acidified potassium manganate (VII) • The heating is performed under reflux which involves heating the reaction mixture in a vessel with a condenser attached to the top • The condenser prevents the volatile alcohol from escaping the reaction vessel as alcohols have low boiling points © copyright Save My Exams CIE IGCSE Chemistry Resources Page 25 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.2.4  CARBOXYLIC ACIDS cont... EXTENDED ONLY cont... Diagram showing the experimental setup for the oxidation with K2MnO4 using reflux apparatus Making esters • Alcohols and carboxylic acids react to make esters in esterification reactions • Esters are compounds with the functional group R-COO-R • Esters are sweet smelling oily liquids used in food flavourings and perfumes • Ethanoic acid will react with ethanol in the presence of concentrated sulfuric acid (catalyst) to form ethyl ethanoate: CH3COOH + C2H5OH → CH3COOC2H5 + H2O © copyright Save My Exams CIE IGCSE Chemistry Resources Page 26 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.2.4  CARBOXYLIC ACIDS cont... Diagram showing the formation of ethyl ethanoate Naming esters • An ester is made from an alcohol and carboxylic acid • The first part of the name indicates the length of the carbon chain in the alcohol, and it ends with the letters ‘- yl’ • The second part of the name indicates the length of the carbon chain in the carboxylic acid, and it ends with the letters ‘- oate’ • E.g. the ester formed from pentanol and butanoic acid is called pentyl butanoate Diagram showing the origin of each carbon chain in ester © copyright Save My Exams CIE IGCSE Chemistry Resources Page 27 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.2.4  CARBOXYLIC ACIDS cont... Examples of esters NAME OF ALCOHOL NAME OF CARBOXYLIC ACID NAME OF ESTER ETHYL PROPANOATE ETHANOL PROPANOIC ACID BUTYL METHANOATE BUTANOL METHANOIC ACID PENTYL ETHANOATE PENTANOL ETHANOIC ACID > NOW TRY SOME EXAM QUESTIONS © copyright Save My Exams CIE IGCSE Chemistry Resources Page 28 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM Page 29 EXAM QUESTIONS ? QUESTION 1 Which of the following formulae shows an alkane? A C2H4 B C4H8 C C4H10 D C5H10 ? QUESTION 2 Which of the equations show the incomplete combustion of methane? A 2 CH4 + 4O2  →  2 CO2 + 4 H2O B CH4 + O2  →  C  +  2 H2O C CH4 + O2  →  C  +  2 H2 D 2 CH4 + 4 O2  →  2 CO2 + 4 H2 ? QUESTION 3 The following reaction takes place in the presence of light. CH4 + Cl2 + light → CH3Cl + HCl What is the name for this reaction? A Combustion B Polymerisation C Thermal decomposition D Substitution > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK Head to savemyexams.co.uk for more questions and revision notes © copyright Save My Exams CIE IGCSE Chemistry Resources REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.3  POLYMERS 14.3.1  POLYMERS Polymers • Polymers are large molecules built by linking 50 or more smaller molecules called monomers • Each repeat unit is connected to the adjacent units via covalent bonds • Some polymers called homopolymers contain just one type of unit • Examples include polythene and polychloroethene, commonly known as PVC • Others contain two or more different types of monomer units and which are called copolymers • Examples include nylon and biological proteins • Different linkages also exist, depending on the monomers and the type of polymerisation • Examples of linkages are covalent bonds, amide links and ester links 14.3.2  SYNTHETIC POLYMERS Plastics & Man-Made Fibres Plastics, nylon and terylene • These are synthetic polymers with many uses • Nylon is a copolymer used to produce clothing, fabrics, nets and ropes • Terylene is a polyester made from monomers which are joined together by ester links • Terylene is used extensively in the textile industry and is often mixed with cotton to produce clothing • Synthetic polymerisation also produces plastics that have many different uses in today’s society. © copyright Save My Exams CIE IGCSE Chemistry Resources Page 30 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.3.2  SYNTHETIC POLYMERS cont... Uses of plastics POLYMER REPEAT UNIT USES POLY(ETHENE) PLASTIC BAGS (LOW I.e. POLYTHENE DENSITY POLYTHENE) PLASTIC BOTTLES (HIGH DENSITY POLYTHENE) POLY(PROPENE) FOOD PACKAGING ROPES CARPETS POLY(CHLOROETHENE) PLASTIC SHEETS I.e. PVC ARTIFICIAL LEATHER DRAINPIPES AND GUTTERS INSULATION ON WIRES Non-biodegradable plastics • These are plastics which do not degrade over time or take a very long time to degrade, and cause significant pollution problems • In particular plastic waste has been spilling over into the seas and oceans and is causing huge disruptions to marine life • In landfills, waste polymers take up valuable space as they are non-biodegradable so microorganisms cannot break them down. This causes the landfill sites to quickly fill up • Polymers release a lot of heat energy when incinerated and produce carbon dioxide which is a greenhouse gas that contributes to climate change • If incinerated by incomplete combustion, carbon monoxide will be produced which is a toxic gas that reduces the capacity of the blood to carry oxygen • Polymers can be recycled but different polymers must be separated from each other which is a difficult and expensive process. © copyright Save My Exams CIE IGCSE Chemistry Resources Page 31 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.3.2  SYNTHETIC POLYMERS cont... EXTENDED ONLY Addition & Condensation Polymers & Deducing Structures Addition polymerisation • Addition polymers are formed by the joining up of many monomers and only occurs in monomers that contain C=C bonds • One of the bonds in each C=C bond breaks and forms a bond with the adjacent monomer with the polymer being formed containing single bonds only • Many polymers can be made by the addition of alkene monomers • Others are made from alkene monomers with different atoms attached to the monomer such as chlorine or a hydroxyl group • The name of the polymer is deduced by putting the name of the monomer in brackets and adding poly- as the prefix • For example if propene is the alkene monomer used, then the name is polypropene Examples of addition polymerisation: polythene and PVC © copyright Save My Exams CIE IGCSE Chemistry Resources Page 32 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.3.2  SYNTHETIC POLYMERS cont... EXTENDED ONLY cont... Condensation polymerisation • Condensation polymers are formed when monomer molecules are linked together with the removal of a small molecule, usually water • Condensation polymerisation usually involves two different monomers, each one having a functional group on each end • Hydrolysing (adding water) to the compound in acidic conditions usually reverses the reaction and produces the monomers by rupturing the peptide link Condensation produces the polyamide which is ruptured at the link by hydrolysis in the reverse reaction Deducing the monomer from the polymer • Polymer molecules are very large compared with most other molecules • Repeat units are used when displaying the formula: • Change the double bond in the monomer to a single bond in the repeat unit • Add a bond to each end of the repeat unit • The bonds on either side of the polymer must extend outside the brackets (these are called extension or continuation bonds) • A small subscript n is written on the bottom right-hand side to indicate a large number of repeat units © copyright Save My Exams CIE IGCSE Chemistry Resources Page 33 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.3.2  SYNTHETIC POLYMERS cont... EXTENDED ONLY cont... Diagram showing the concept of drawing a repeat unit of a monomer Deducing the polymer from the monomer • Identify the repeating unit in the polymer • Change the single bond in the repeat unit to a double bond in the monomer • Remove the bond from each end of the repeat unit and the subscript n Diagram showing how to deduce the structure of a monomer from a repeat unit Example: Deducing the structure of chloroethene from a repeat unit of Poly(chloroethene) Diagram showing the monomer from the repeat unit of an addition polymer (polychloroethene) © copyright Save My Exams CIE IGCSE Chemistry Resources Page 34 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.3.2  SYNTHETIC POLYMERS cont... EXTENDED ONLY cont... Formation of Nylon • Nylon is a polyamide made from dicarboxylic acid monomers (a carboxylic with a -COOH group at either end) and diamines (an amine with an -NH2 group at either end) • Each -COOH group reacts with another -NH2 group on another monomer • An amide linkage is formed with the subsequent loss of one water molecule per link The condensation reaction in which the polyamide Nylon is produced © copyright Save My Exams CIE IGCSE Chemistry Resources Page 35 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.3.2  SYNTHETIC POLYMERS cont... EXTENDED ONLY cont... Formation of Terylene • Terylene is a polyester made from dicarboxylic acid monomers (a carboxylic with a -COOH group at either end) and diols (an alcohol with an -OH group at either end) • Each -COOH group reacts with another -OH group on another monomer • An ester linkage is formed with the subsequent loss of one water molecule per link The condensation reaction in which the polyester Terylene is produced EXAM TIP You should be able to draw the box diagrams representing polymers where each box represents a part of the repeating hydrocarbon chain. The functional groups on the monomers and the link formed in the polymers are the important parts and must be clearly drawn. © copyright Save My Exams CIE IGCSE Chemistry Resources Page 36 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.3.3  NATURAL POLYMERS Proteins Proteins and carbohydrates • These are two of the main and most important components of food • Carbohydrates provide energy which is released during cellular respiration • Proteins are the building blocks of cells and are essential for growth and all of the enzyme catalysts in the body are proteins Proteins • Proteins are condensation polymers which are formed from amino acid monomers joined together by peptide bonds, similar to the structure in Nylon • The units in proteins are different however, consisting of amino acids • Amino acids are small molecules containing NH2 and COOH functional groups • Most proteins contain at least 20 different amino acids • These are the monomers which polymerise to form the protein Diagram showing condensation polymerisation to produce a protein Diagram showing a peptide link which holds proteins together © copyright Save My Exams CIE IGCSE Chemistry Resources Page 37 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.3.3  NATURAL POLYMERS cont... Hydrolysis of proteins • Proteins can be hydrolysed by the addition of water in acidic or alkaline conditions • Heat and concentrated acid (usually 6 mol/dm3 HCl) are used with a reflux condenser to prevent the acidic vapours from escaping the reaction vessel • Aqueous ammonia is added after completion to neutralise the excess acid • Enzymes can also be used to hydrolyse some proteins at room temperature, mimicking natural bodily processes Diagram showing the rupture of a peptide link by hydrolysis EXAM TIP When drawing biological polymers it is important that you show the peptide link clearly in your sketch. © copyright Save My Exams CIE IGCSE Chemistry Resources Page 38 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM 14.3.3  NATURAL POLYMERS cont... EXTENDED ONLY Carbohydrates, Fermentation & Chromatography Carbohydrates • Carbohydrates are compounds of carbon, hydrogen and oxygen with the general formula Cx(H2O)y • There are simple carbohydrates and complex carbohydrates • Simple carbohydrates are called monosaccharides and are sugars such as fructose and glucose • Complex carbohydrates are called polysaccharides such as starch and cellulose. These are condensation polymers formed from simple sugar monomers • Complex carbohydrates, unlike proteins, are usually made up of the same monomers • A H2O molecule is eliminated when simple sugars polymerise. The linkage formed is an -O- linkage called a glycosidic linkage Diagram of a polysaccharide showing the glycosidic linkages (-O-) binding the monomers together Hydrolysis of carbohydrates • The complex carbohydrates also undergo hydrolysis and produce the simple sugar monomers from which they were made • This can be done by refluxing with more moderately concentrated HCl Fermentation of simple sugars • Simple sugars can be fermented to produce alcohol • They are dissolved in water and yeast is added to be fermented between 15 and 35°C in the absence of oxygen for a few days • If the temperature is too low the reaction rate will be too slow and if it is too high the enzymes will become denatured © copyright Save My Exams CIE IGCSE Chemistry Resources Page 39 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY 14.3.3  NATURAL POLYMERS cont... EXTENDED ONLY cont... • Yeast contains zymase enzymes (biological catalysts) that break down starch or sugar to glucose • The yeast respires anaerobically using the glucose to form ethanol and carbon dioxide: C6H12O6 + Enzymes → 2CO2 + 2C2H5OH Chromatography • The identification of the products of the hydrolysis of carbohydrates and proteins can be done using chromatography • Originally used for separating coloured substances, chromatography can be used to identify colourless compounds using locating agents • Both carbohydrate and protein monomers are colourless so locating agents must be used • A technique called 2-Dimensional paper chromatography is used as some simple sugars and amino acids have the same Rf • In this technique a run is carried out in one direction, then the paper is rotated by 90º and performed again using a different solvent • This further separates sample spots that may not have separated in the first run • The resulting chromatogram is dried and sprayed with a locating agent • The Rf value of each solvent used is characteristic for each sugar or amino acid Diagram showing the procedure for performing 2-Dimensional paper chromatography > NOW TRY SOME EXAM QUESTIONS © copyright Save My Exams CIE IGCSE Chemistry Resources Page 40 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 2 O1R4GOANRISGAATNIOINCOCFHTEHEMOISRGTARNYISM EXAM QUESTIONS ? QUESTION 1 Which statement about polymers is correct? A Addition polymers are all biodegradable. B Condensation polymers can all be hydrolysed to give amino acids. C Condensation polymers only exist in nature. D Forming addition polymers produces only one product. ? QUESTION 2 A macromolecule is a very large molecule. Macromolecules can be made by joining smaller molecules together. This is called polymerisation. Which row in the table describes the formation of a polymer? monomer polymer A ethane poly(ethane) B ethene poly(ethene) C ethane poly(ethene) D ethene poly(ethane) © copyright Save My Exams CIE IGCSE Chemistry Resources Page 41 REVISION NOTES TOPIC QUESTIONS PAST PAPERS

CIE IGCSE Chemistry Revision Notes savemyexams.co.uk YOUR NOTES 14 ORGANIC CHEMISTRY EXAM QUESTIONS ? QUESTION 3 The diagram shows three repeat units in the structure of an addition polymer. Which alkene monomer is used to make this polymer? > CHECK YOUR ANSWERS AT SAVEMYEXAMS.CO.UK Head to savemyexams.co.uk for more questions and revision notes © copyright Save My Exams CIE IGCSE Chemistry Resources Page 42 REVISION NOTES TOPIC QUESTIONS PAST PAPERS